Logic circuitry powered by partially rectified ac waveform

ABSTRACT

Logic circuitry is powered by a partially rectified alternating current (ac) waveform. The waveform is partially rectified in the sense that it does not provide a clean, primarily dc power signal. Instead, it is possible to power logic circuitry with a waveform that includes a substantial ac component. The partially rectified ac waveform may be applied to logic circuitry incorporating thin film transistors based on amorphous or polycrystalline organic semiconductors, inorganic semiconductors or combinations of both.

FIELD

The invention relates to logic circuitry and, more particularly,techniques for powering logic circuitry.

BACKGROUND

Thin film circuit devices, including transistors, diodes, and the like,are widely used to form logic circuitry in a variety of modernelectronic devices, including integrated circuits, flat panel displays,smart cards, and radio frequency identification (RFID) tags. Thin filmcircuit devices are formed by depositing, masking and etching a varietyof conducting, semiconducting and insulating layers to form a thin filmstack.

Typically, thin film transistors (TFTs) are based on inorganicsemiconductor materials such as amorphous silicon or cadmium selenide.More recently, significant research and development efforts have beendirected to the use of organic semiconductor materials to form thin filmtransistor circuitry.

Organic semiconductor materials offer a number of manufacturingadvantages for transistor fabrication including low processingtemperatures. In particular, organic semiconductor materials permit thefabrication of organic thin film transistors (OTFTs) on flexiblesubstrates such as thin glass, polymeric or paper-based substrates.

In addition, organic semiconductor materials can be formed usinglow-cost fabricaton techniques such as printing, embossing or shadowmasking. Although the performance characteristics of OTFTs have improvedwith continued research and development, device performance andstability continue to present challenges.

SUMMARY

In general, the invention is directed to logic circuitry powered by apartially rectified alternating current (ac) waveform. The waveform ispartially rectified in the sense that it does not provide a clean,primarily dc power waveform. Instead, it is possible to power logiccircuitry with a waveform that includes a substantial ac component. Infact, the dc component would not be sufficient, on its own, to power thecircuit. The invention may be applied to logic circuitry incorporatingthin film transistors based on amorphous or polycrystalline organicsemiconductors, inorganic semiconductors or combinations of both.

Enhanced stability may permit the use of OTFT circuitry to form avariety of thin film transistor-based logic circuit devices, includinginverters, oscillators, logic gates, registers, and othertransistor-based logic circuits. Such logic circuit devices may findutility in a variety of applications, including integrated circuits,flat panel displays, smart cards, and circuits. For some applications,powering logic circuitry with a partially rectified ac waveform mayeliminate the need for a full wave ac-dc rectification stage.

A partial rectification stage may be realized by a diode, a transistor,or the like, without the need for a filtering capacitor. In this manner,the invention may reduce the manufacturing time, expense, cost,complexity, and size of the component carrying the logic circuitrypowered by the partially rectified ac power waveform. With partialrectification both and ac and dc component exist. The ac portion may bequite substantial and the dc portion may be small. The dc portion, inthis case, may be insufficient to power a logic circuit by itself.Typically logic circuits require voltages in excess of the thresholdvoltages of the transistors that make up the logic circuit. In a dcpowered circuit, if the dc voltage is less than the threshold voltage,the circuit will not operate. With ac powering it is possible to havethe dc component less than the threshold voltage, if the ac component issufficiently large, and still power the circuit.

The partially rectified ac power waveform directly powers the logic gatecircuitry. In particular, the ac power source and partial rectificationstage apply a partially rectified ac power waveform to one or moreindividual logic gates, instead of applying dc power to the logic gates.

The partial rectification stage may include a half-wave or full-waverectifier with insufficient capacitive filtering to produce a primarilydc power signal as the partially rectified ac power waveform. In thismanner, the large filtering capacitor ordinarily provided in a full-waveor half-wave rectification stage can be eliminated or reduced in size sothat the overall size of the circuit can be reduced.

Logic circuitry powered by a partially rectified ac power waveform maybe used in a variety of electronic devices. As an example, such logiccircuitry may be especially useful in applications directed to radiofrequency (RFID) tags in which an ac waveform is induced by near-fieldelectromagnetic radio frequency coupling. The ac waveform can bepartially rectified to power some or all of the electronic logiccircuitry carried by the circuit.

In one embodiment, the invention provides an electronic circuitcomprising a first transistor and a second transistor arranged to form alogic gate, an alternating current (ac) source to generate an ac powerwaveform, and a partial rectification stage to produce a partiallyrectified ac power waveform from the ac power waveform and directlypower the logic gate with the partially rectified ac power waveform. Thelogic gate may be characterized by a propagation delay. The ac waveformhas a period less than the propagation delay, and preferably less thanone fifth of the propagation delay.

In another embodiment, the invention provides a method comprisingdirectly powering a logic gate formed by at least a first transistor anda second transistor with a partially rectified alternating current (ac)power waveform produced from an alternating current (ac) power source.

In an added embodiment, the invention provides a radio frequencyidentification (RFID) tag comprising a logic gate formed by at least afirst transistor and a second transistor, a radio frequency (RF) energycoupling device to provide an ac power waveform, and a partialrectification stage that produces a partially rectified ac powerwaveform from the ac power waveform and directly powers the logic gatewith the partially rectified ac power waveform.

In a further embodiment, the invention provides a radio frequencyidentification (RFID) system comprising an circuit including first andsecond transistors arranged to form a logic gate, a radio frequency (RF)converter that converts RF energy to an alternating current (ac) powerwaveform, a partial rectification stage that produces a partiallyrectified ac power waveform from the ac power waveform and directlypowers the logic gate with the partially rectified ac power waveform,and a modulator that conveys information, and an RFID reader thattransmits the RF energy to the circuit for conversion by the RFconverter, and reads the information conveyed by the modulator.

The invention can provide a number of advantages. For example, the useof a partially rectified ac power waveform to directly power logiccircuitry may eliminate the need for a filtering capacitor in a fullwave rectifier or half wave component, which is commonly required inmany applications for delivery of dc power to the circuitry. Accordinglythe use of partially rectified ac power may reduce the manufacturingtime, expense, cost, complexity, and size of components carrying thinfilm transistor circuitry.

For circuits, as a particular example, the use of ac-powered thin filmcircuitry may substantially reduce the cost and size of the tag byeliminating or reducing the size of many of the components typicallyassociated with an ac-dc rectifier stage, including diode or transistorbridges, and large filtering capacitors. By reducing the complexity ofthe rectifier stage, thin film logic circuitry powered by a partiallyrectified ac waveform can result in substantial cost savings and sizereductions in the design and manufacture of the circuit.

Additional details of these and other embodiments are set forth in theaccompanying drawings and the description below. Other features, objectsand advantages will become apparent from the description and drawings,and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a circuit diagram illustrating a digital logic circuit poweredby a partially rectified ac waveform.

FIG. 2 is a circuit diagram illustrating an inverter circuit powered bya partially rectified ac waveform generated by a half-wave diode-basedpartial rectification stage.

FIG. 3 is a circuit diagram illustrating an inverter circuit powered bya partially rectified ac waveform generated by a half-wavetransistor-based partial rectification stage.

FIGS. 4A, 4B and 4C are graphs conceptually illustrating an ac powerwaveform and exemplary partially rectified ac power waveforms.

FIG. 5 is a circuit diagram illustrating a NAND gate circuit powered bya partially rectified ac waveform generated by a half-wave diode-basedpartial rectification stage.

FIG. 6 is a circuit diagram illustrating a NAND gate circuit powered bya partially rectified ac waveform generated by a half-wavetransistor-based partial rectification stage.

FIG. 7 is circuit diagram of a NOR gate circuit powered by a partiallyrectified ac waveform.

FIG. 8 is a circuit diagram illustrating a thin film transistor-basedring oscillator circuit powered by a partially rectified ac waveformgenerated by a half-wave transistor-based rectifier stage with afiltering capacitor.

FIG. 9 is a circuit diagram illustrating a thin film transistor-basedring oscillator circuit powered by a partially rectified ac waveformgenerated by a half-wave transistor-based rectifier stage without afiltering capacitor.

FIG. 10 is a block diagram illustrating application of ac-powered thinfilm transistor circuitry in an circuit/reader system.

FIG. 11 is a circuit diagram further illustrating the circuit/readersystem of FIG. 10.

FIG. 12 is a circuit diagram further illustrating a reader associatedwith the circuit/reader system of FIG. 10.

FIG. 13 is a circuit diagram illustrating an inverter circuit powered bya partially rectified ac waveform to drive a liquid crystal displayelement.

FIG. 14 is a circuit diagram illustrating an inverter circuit powered bya partially rectified ac waveform to drive a light emitting diode (LED).

DETAILED DESCRIPTION

FIG. 1 is a circuit diagram illustrating a circuit 10 powered by apartially rectified ac waveform. As shown in FIG. 1, an ac power supply12 delivers an ac power waveform to a partial rectification stage 14.Partial rectification stage 14 partially rectifies the ac power waveformto power a digital logic circuit 16. A signal source 18 drives digitallogic circuit 16 with a logic signal. Digital logic circuit 16 producesan output logic signal at output 20. A capacitor 22 may be coupledbetween output 20 and ground.

The waveform applied to digital logic circuit 16 by partialrectification stage 14 is partially rectified in the sense that it doesnot provide a clean, primarily dc power signal, as would conventionallybe used to power a digital logic circuit. Instead, in accordance withthe invention, it is possible to power digital logic circuit 16 with awaveform that includes a substantial ac component.

A partially rectified waveform may be applied, for example, to a digitallogic circuit 16 incorporating thin film transistors based on amorphousor polycrystalline organic semiconductors, inorganic semiconductors orcombinations of both. The use of a partially rectified ac power waveformto power digital logic circuit 16 can support satisfactory deviceperformance for a variety of applications. For example, when OTFTcircuitry is powered by a partially rectified ac power waveform, theOTFT circuitry may exhibit satisfactory performance characteristics evenwithout a dc power signal.

Satisfactory performance without a clean dc power signal may permit theuse of TFT circuitry, without the need for full wave rectificationcircuitry, to form a variety of thin film transistor-based logic circuitdevices, including inverters, oscillators, logic gates, registers, orany other transistor-based logic circuit. Such logic circuit devices mayfind utility in a variety of applications, including integratedcircuits, flat panel displays, smart cards, and circuits.

FIG. 2 is a circuit diagram illustrating an inverter circuit 16A poweredby a partially rectified ac waveform generated by a half-wavediode-based partial rectification stage 14A. As shown in FIG. 2, a diode26 serves to pass only the negative-going half cycles of the ac waveformgenerated by ac power source 12, and thereby functions as a partialrectification stage 14A. In this example, inverter circuit 16A includesa load transistor 28 and a drive transistor 30. Each transistor 28, 30may be a thin film field effect transistor (FET), and may be based on anamorphous or polycrystalline inorganic or organic semiconductingmaterial, or a combination of both. A capacitor 22 may be coupledbetween output 20 and ground.

Useful organic semiconductor materials for forming OTFTs include acenesand substituted derivatives thereof. Particular examples of acenesinclude anthracene, naphthalene, tetracene, pentacene, and substitutedpentacenes (preferably pentacene or substituted pentacenes, includingfluorinated pentacenes). Other examples include semiconducting polymers,perylenes, fullerenes, phthalocyanines, oligothiophenes, polythiophenes,polyphenylvinylenes, polyacetylenes, metallophthalocyanines andsubstituted derivatives. Useful bis-(2-acenyl) acetylene semiconductormaterials are described in copending application U.S. Ser. No.10/620027, filed on Jul. 15, 2003, which is herein incorporated byreference. Useful acene-thiophene semiconductor materials are describedin copending application U.S. Ser. No. 10/641730, filed on Aug. 15,2003, which is herein incorporated by reference. Useful inorganicsemiconductor materials for forming thin film transistors includeamorphous silicon, polysilicon, tellurium, zinc oxide, zinc selenide,zinc sulfide, cadmium sulfide, and cadmium selenide.

As an alternative, digital logic circuit 16A may be formed by acombination of organic and inorganic semiconducting material, e.g., toform a complementary metal oxide semiconductor (CMOS) inverter circuit.For example, in some applications, inverter circuit 16A may be formed byan n-channel metal oxide semiconductor (NMOS) inorganic field effecttransistor (FET) and a p-channel metal oxide semiconductor (PMOS)organic field effect transistor (FET). When OTFTs are used, transistors28, 30 may be especially adaptable to fabrication using low costfabrication techniques, and may be formed on flexible substrates forsome applications.

The ac power source 12 directly applies an ac power waveform to diode26, which applies a partially rectified waveform, in the form of aseries of alternating half cycles of the ac waveform, to invertercircuit 16A. In some embodiments, a filtering capacitor may be providedbetween the cathode of diode 26 and ground. However, the filteringcapacitor may have insufficient capacitance to produce a fullyrectified, substantially dc waveform. Rather, diode 26 produces only apartially rectified ac waveform that is applied directly to inverter16A.

In this manner, inverter 16A receives only a partially rectified acpower waveform instead of a dc power waveform. In other words, inverter16A operates in response to the partially rectified ac power waveform.Accordingly, intervening circuitry may exist between ac power source 12,diode 26 and inverter 16A provided that the inverter still receives onlya partially rectified ac power waveform as operating power, rather thana dc power signal. In the example of FIG. 1, the partially rectified acpower waveform is applied directly across the common gate and drainconnection of load transistor 28 and the ground connection coupled tothe source of drive transistor 30.

FIG. 3 is a circuit diagram illustrating an inverter circuit 16A poweredby a partially rectified ac waveform generated by a half-wavetransistor-based partial rectification stage 14B. As shown in FIG. 3,partial rectification stage 14B includes a transistor 34. The gate anddrain of transistor 34 are coupled in common to the positive terminal ofac power supply 12. The source of transistor 34 is coupled to create anoutput node for partial rectification stage 14B. The output node ofpartial rectification stage 14B is coupled to both the gate and drain ofload transistor 28 of inverter circuit 16A. Hence, the circuit of FIG. 3substantially corresponds to the circuitry of FIG. 2, but includes atransistor-based partial rectification stage 14B. Transistor 34 may be athin film field effect transistor (FET), and may be based on anamorphous or polycrystalline inorganic or organic semiconductingmaterial, or a combination of both.

Again, the use of a partially rectified power waveform to power thinfilm transistor-based logic circuitry, such as inverter 16A in FIGS. 2and 3, can support satisfactory device performance for a variety ofapplications, while enhancing long-term stability of the circuitry. Forexample, when inverter 16A is powered by a partially rectified acwaveform, the inverter may exhibit satisfactory performancecharacteristics relative to dc-powered inverters. Also, operation ofinverter 16A with a partially rectified ac waveform eliminates the needfor an ac-dc full wave rectification stage.

As shown in FIG. 3, the gate and drain of load transistor 28 are coupledto receive the partially rectified ac waveform produced by partialrectification stage 14B. In particular, the gate and drain of loadtransistor 28 are both coupled to the source of transistor 34. The drainof drive transistor 30 is coupled to the source of load transistor 28,and the source of the drive transistor is coupled to ground. Signalsource 18 generates a logic signal to drive the gate of drive transistor30.

In response, inverter 16A produces an inverted output 20, which may beoutput across a load capacitor 22. Load capacitor 22 may serve to filterout some of the ac voltage present at the inverted output 20 andprovides for a cleaner output logic signal. The amount of filteringdepends on the capacitance of load capacitor 22 and the frequency of theac power. Load capacitor 22 may be formed by an input capacitanceproduced by gate/source overlap within a logic gate coupled to output 20in the event inverter 16A is coupled to drive one or more additionallogic gates.

The gate/source overlap may be controlled during manufacture of a drivetransistor in a subsequent logic gate to produce a desired level ofcapacitance in load capacitor 22. Alternatively, load capacitor 22 maybe formed independently, particularly if output 20 does not driveanother logic gate.

In some embodiments, load transistor 28 may have a gate width to gatelength ratio that is greater than or equal to a gate width to gatelength ratio of the drive transistor 30. In this case, direct current(dc) powering of the circuit could result in inferior operation of thelogic gate, for NMOS or PMOS designs, because of the reduced gain. NMOSor PMOS ring oscillators based on this design, for example, would beunstable. An added benefit of having the gate width to gate length ratioof load transistor 28 greater or equal to the gate width to gate lengthratio of drive transistor 30 is that the total circuit area is reduced.

Notably, although the inverted output 20 may be filtered by loadcapacitor 22, the input power waveform applied to inverter 16A generallyis not. In particular, the partially rectified ac waveform produced bypartial rectification stage 14B is not filtered to an extent sufficientto produce a primarily dc signal for inverter 16A. Rather, the partiallyrectified waveform produced by partial rectification stage 14B includesa substantial ac component.

In some embodiments, a relatively small filtering capacitor may becoupled between the source of transistor 34 and ground, but thecapacitance is generally insufficient to entirely filter out variationin the partially rectified waveform due to non-rectified portions of theac power waveform produced by ac power supply 12. In particular,portions of the partially rectified waveform that are coincident withthe non-rectified negative half cycles produced by ac power supply 12will still present substantial variation in partially rectifiedwaveform. In this manner, the large filtering capacitor ordinarilyprovided in a full-wave or half-wave rectification stage can beeliminated or reduced in size so that the overall size of the circuit orelectronic device can be reduced.

FIGS. 4A, 4B and 4C are graphs conceptually illustrating an ac powerwaveform and exemplary partially rectified ac power waveforms. FIG. 4Adepicts an ac power waveform 21 produced by ac power supply 12. As shownin FIG. 4A, the ac power waveform is substantially sinusoidal andincludes positive half cycles 23, 25 and negative half cycles 27. Inaccordance with the invention, a partial rectification stage 14partially rectifies the ac power waveform 21 to produce a partiallyrectified ac waveform, e.g., as depicted in FIGS. 4B or 4C.

In the example of FIG. 4B, partial rectification stage 14 produces apartially rectified ac power waveform 29A, essentially by half-waverectification without sufficient capacitive filtering to produce aprimarily dc signal. Instead, partially rectified ac power waveform 29Aincludes positive half cycle 31 and positive half cycle 33, buteliminates any negative half cycles and drops to a reference voltagelevel. Hence, according to the example of FIG. 4B, partial rectificationstage 14 may include substantially no capacitive filtering. As a result,the partially rectified waveform 29A essentially preserves, in halfcycles 31, 33, the waveform characteristics of the positive half cycles23, 25 of the ac power waveform 21. Line 130 represents the average dcvoltage, and is insufficient to power the circuit.

In the example of FIG. 4C, partial rectification stage 14 produces apartially rectified ac power waveform 29B with positive half cycles 35,37. In addition, partial rectification stage 14 may include a limitedamount of capacitive filtering that creates an exponential tail off 39,41 following each half cycle 35, 37. The peaks of half-cycles 35 and 37represent sufficient voltages to power the circuit. The capacitivefiltering, in some embodiments, may be provided by a capacitor placedbetween an output of partial rectification stage 14 and ground. As shownin FIG. 4C, the capacitance is insufficient to produce a primarily dcpower signal. Rather, the partially rectified waveform 29B may preservea substantial ac component of the original ac power supply waveform 21(FIG. 4A) produced by ac power supply 12. Line 131 represents theaverage dc voltage, and is insufficient to power the circuit.

For some applications, powering a logic circuit 16 with a partiallyrectified ac waveform eliminates the need for a full wave or half-waveac-dc rectification stage that produces a dc component sufficient topower the circuit. Instead, a power source may include a relativelysimple partial rectification stage 14. As illustrated in FIGS. 2 and 3,a partial rectification stage 14 may be realized by a diode, atransistor, or the like, without the need for a large filteringcapacitor. In this manner, the invention may reduce the manufacturingtime, expense, cost, complexity, and size of the component carrying thelogic circuitry powered by the partially rectified ac power waveform.

Logic circuitry powered by a partially rectified ac power waveform maybe used in a variety of electronic devices. As one example, such logiccircuitry may be especially useful in applications directed to radiofrequency (RFID) tags in which an ac waveform is induced by radiofrequency coupling. The ac waveform can be partially rectified to powersome or all of the electronic logic circuitry carried by the circuit. Byeliminating circuitry ordinarily required by a full-wave or half-waverectifier, including the sizable capacitor often used with a half-waverectifier, the size of the circuit may be significantly reduced. Similarsize reductions may be achieved in other types of electronic devices.

FIG. 5 is a circuit diagram illustrating a thin film transistor-basedNAND gate circuit 38 powered by a partially rectified ac waveformgenerated by a half-wave diode-based partial rectification stage 14A. Asshown in FIG. 5, a NAND gate 40 includes a load transistor 28 and drivetransistors 30A, 30B. The gate and drain of load transistor 28 arecoupled to the output of partial rectification stage 14A, which includesa diode 26.

The drain of first drive transistor 30A is coupled to the source of loadtransistor 28. The drain of second drive transistor 30B is coupled tothe source of first drive transistor 30A. The source of second drivetransistor 30B is coupled to ground. First and second signal sources18A, 18B drive the gates of drive transistors 30A, 30B, respectively. Inresponse, transistors 28, 30A, 30B form a NAND gate 40 that produces alogical NAND output 20.

NAND circuit 40 of FIG. 5 is operative in response to the partiallyrectified ac power waveform produced by diode 26. In particular, thepartially rectified ac power waveform is coupled directly to NAND gate40. In some embodiments, a load capacitor may be coupled across output20. The load capacitor may be formed independently or realized by theinput capacitance of a logic gate driven by output 20 of NAND gate 40.Also, a filtering capacitor may be placed between the cathode of diode26 and ground, provided that the resulting capacitance is insufficientto produce a primarily dc power signal.

FIG. 6 is a circuit diagram illustrating a NAND gate circuit 42 poweredby a partially rectified ac waveform generated by a half-wavetransistor-based partial rectification stage 14B. NAND gate circuit 42includes NAND gate 40 and corresponds substantially to NAND circuit 38of FIG. 5, but incorporates a transistor-based partial rectificationstage 14B with transistor 34.

Transistor-based partial rectification stage 14B may be identical topartial rectification stage 14B of FIG. 3. As in the example of FIG. 5,a load capacitor may be coupled across output 20 in circuit 42 of FIG.6. In addition, a filtering capacitor may be placed between the outputof partial rectification 14B and ground, provided that the resultingcapacitance is insufficient to produce a primarily dc power signal.

FIG. 7 is a circuit diagram illustrating a thin film transistor-basedNOR gate circuit 44 with a NOR gate 46 powered by a partially rectifiedac waveform. FIG. 7 represents another example of a thin filmtransistor-based logic circuit that operates with a partially rectifiedac waveform produced by a partial rectification stage 14. As shown inFIG. 7, transistors 28, 50A, and 50B form NOR gate 46. The drains offirst and second drive transistors 50A, 50B are coupled to the source ofload transistor 28, and to output 20.

The sources of first and second drive transistors 50A, 50B are coupledto ground. First and second signal sources 48A, 48B drive the gates ofdrive transistors 50A, 50B, respectively. In response, NOR gate 46produces a logical NOR output 20. NOR circuit 46 is operative inresponse to the partially rectified ac power waveform delivered bypartial rectification stage 14. In some embodiments, a load capacitormay be coupled across logical NOR output 20. Again, the load capacitormay be formed independently or realized by the input capacitance of alogic gate driven by output 20 of NOR circuit 44.

FIGS. 8 and 9 are circuit diagrams illustrating ac-powered thin filmtransistor-based ring oscillator circuits 51, 53, respectively. Ringoscillator circuits 51 and 53 are examples of another circuit that canbe implemented using logic gates powered by a partially rectified acpower waveform, e.g., including inverter stages based on OTFTs, whichmay be formed on flexible substrates. As shown in FIGS. 8 and 9, ringoscillator circuits 51 and 53 include an odd number of inverter stagesarranged in series. In the example of FIGS. 8 and 9, ring oscillatorcircuits 51 and 53 include seven inverter stages 52A-52G having,respectively, load transistors 54A-54G and drive transistors 56A-56G,respectively.

Each transistor 54 and 56 in ring oscillator circuits 51 and 53 is athin film field effect transistor powered by a partially rectified acwaveform. For example, ac power source 12 delivers ac power to partialrectification stage 14B. In the examples of FIGS. 8 and 9, partialrectification stage 14B is a transistor-based partial rectificationstage, although a diode-based partial rectification stage or otherconfiguration may be used. The source of transistor 34 in partialrectification stage 14B is coupled to drive the common gate-drain nodeof load transistor 54A in first inverter stage 52A. In the example ofFIG. 8, a filtering capacitor 55 may optionally be provided in ringoscillator circuit 51A between the output of partial rectification stage14B and ground. In FIG. 9, a filtering capacitor 55 is not provided inring oscillator circuit 51B.

In the example of FIGS. 8 and 9, each inverter stage 52A-G has an outputthat is optionally coupled across a respective load capacitor 58A-58G.For example, the output of inverter stage 52A may be coupled across loadcapacitor 58B, and the output of inverter stage 52G may be coupledacross load capacitor 58A. In other embodiments, load capacitors 58 maybe omitted. Each capacitor 58 may be formed by the input capacitanceproduced by gate/source overlap within a drive transistor 56 of asubsequent inverter stage 52 that is driven by the output of arespective inverter stage.

The output 60 of final inverter stage 52G is coupled to the gate ofdrive transistor 56A in first inverter stage 52A to provide feedback.Ring oscillator circuit 51, 53 of FIGS. 8 and 9 operates in response tothe partially rectified ac power supply waveform delivered by partialrectification stage 14B. During operation, ring oscillator circuit 51provides a clock signal. For example, the output of each inverter stage52 in ring oscillator circuit 51, 53 can be tapped to provide a clocksignal with a desired phase.

In general, the output waveform produced by ring oscillator circuit 51,53 will have a frequency that is dependent on the number of inverterstages 52 and the propagation delays produced by the individual inverterstages. The propagation delay is inversely related to the voltage of thepartially rectified ac waveform applied to ring oscillator circuit 51,53 and the mobility of the semiconducting material, and proportional toany applicable parasitic or external capacitance present in inverterstages 52.

Operation of thin film transistor circuitry, such as ring oscillatorcircuits 51, 53, may be possible with high ac power supply frequencies.Functioning ring oscillator circuits that conform substantially tocircuits 51, 53 may operate, for example, with ac power supplyfrequencies on the order of several hundred kHz to 6 MHz or higher. Withincreased semiconductor mobility, it may be reasonable to expect use ofring oscillator circuits, powered by partially rectified ac powerwaveforms as described herein, with ac power supply frequencies ofgreater than 10 MHz.

FIG. 10 is a block diagram illustrating application of thin filmtransistor-based circuitry powered by a partially rectified ac powerwaveform in an circuit/reader system 66. Use of ac-powered thin filmtransistor-based circuitry may be particularly desirable in an circuitfor a number of reasons, as will be described. As shown in FIG. 10, acircuit system 66 may include a reader unit 68 and an circuit 70.

Reader unit 68 may include a radio frequency (RF) source 74 and a reader72. RF source 74 transmits RF energy to circuit 70 to provide a sourceof power. In this manner, circuit 70 need not carry an independent powersupply, such as a battery. Instead, circuit 70 is powered across awireless air interface between reader unit 68 and the circuit. To thatend, reader unit 68 includes an inductor 76 that serves, in effect, asan antenna to transmit and receive RF energy.

As further shown in FIG. 10, circuit 70 may include an ac power source73. As will be explained, ac power source 73 may serve to convert RFenergy transmitted by reader unit 68 into ac power for delivery to thinfilm transistor circuitry carried by circuit 70. circuit 70 may receivethe RF energy from reader unit 68 via an inductor 78 that serves as areceiver.

Inductor 78 serves as a radio frequency (RF) energy coupling device toprovide an ac power waveform for ac power source 73 based on RF energyabsorbed from RF energy transmitted by reader unit 68. A capacitor (notshown) also may be provided in parallel with inductor 78, if desired.

A partial rectification stage 80 receives an ac waveform from inductor78 and produces a partially rectified ac waveform to power digital logiccircuitry within circuit 70. circuit 70 further includes a modulationoutput inverter 82, an output buffer circuit 84, control logic 86, clockcircuit 88 and data circuit 90, one or more of which may be formed by anarrangement of thin film transistor circuitry.

Clock 88 drives control logic circuit 86 to output data from datacircuit 90, which may comprise a plurality of data lines carrying anidentification code. Output buffer 84 buffers the output from controllogic 86. Modulation inverter 82, in turn, modulates the buffered outputfor interpretation by reader unit 68 via inductors 76, 78. For example,modulation inverter 82 conveys the information by modulating the signalapplied across inductor 78.

FIG. 11 is a circuit diagram further illustrating the circuit/readersystem 66 of FIG. 10. As shown in FIG. 11, RF source 74 may include anac generator 92 that transmits an ac output signal via inductor 76. Forsome applications, ac generator 92 may take the form of a sinusoidalcurrent source with an output of approximately 0 to 5 amps at afrequency of approximately 125 kHz.

Inductors 76 and 78 form a transformer for electromagnetic coupling ofRF energy between RF source and circuit 70. Resistor 94 is selected tolimit current. A capacitor 96 may be placed in parallel with inductor 78within power source 73 to form a parallel resonant tank that governs thefrequency of the power source according to the equation:$f = {\frac{1}{2\pi\sqrt{LC}}.}$where L is the inductance of inductor 78 and C is the capacitance ofcapacitor 96.

With an inductance of 50 μH and a capacitance of 32 nF, inductor 78 andcapacitor 96 generate a resonant frequency of approximately 125 KHz.Hence, in this example, the output of ac power source 73 is a sinusoidalwaveform with a frequency of approximately 125 kHz. This waveformproduced by inductor 78 is partially rectified by partial rectificationstage 80 to produce a partially rectified ac power waveform as theoutput of power source 73. The partially rectified ac power waveform isthen applied to clock circuit 88, control logic 86, data lines 90,output buffer 84, and modulation inverter 82 as represented in FIG. 11by the terminals POWER and COMMON.

FIG. 11 depicts an circuit 70 that carries an n-bit identification code.For ease of illustration, circuit 70 carries a 7-bit identification codespecified by data lines 70. In many applications, circuit 70 may carry amuch larger identification code, e.g., 31-bit, 63-bit or 127-bit codes.In some embodiments, selected data lines 90 may carry information usedfor start bit identification, data stream synchronization and errorchecking. In the example of FIG. 11, clock circuit 88 is a ringoscillator formed by a series of seven inverter stages arranged in afeedback loop.

The ring oscillator of FIG. 11 may be similar to ring oscillator 51 or53 of FIGS. 8 and 9. The outputs of two successive inverters are appliedto a respective NOR gate provided in control logic 86. In this way,seven NOR gates are used to generate a sequence of seven pulses withineach clock cycle produced by the ring oscillator. Note that the numberof NOR gates in control logic 86 may vary. Again, this arrangement couldbe extended, in principle, to larger numbers of bits, e.g., n=31, 63 or127.

Switches shown in series with data lines 90 are connected to respectiveNOR gate outputs at one end. If a switch is closed, the respective dataline couples the NOR gate output to ground If the switch is open, theNOR gate output is coupled as one of the inputs to a 7-input OR gatewithin control logic 86.

In the example of FIG. 11, the switches for second and fourth data lines(from left to right) are closed. As a result, data lines 90 store the7-bit identification code “1010111.” The switches can be made, forexample, from metal lines that extend from the NOR gate outputs toground. The electrical connections to ground can be intentionally brokenor connected during manufacturing to produce, in effect, an open switch,and thereby encode a unique identification code into data lines 90 ofcircuit 70. The electrical connections may be broken by a variety ofmanufacturing techniques such as, for example, laser etching, mechanicalscribing, or electrical fusing.

The output of the 7-input OR gate in control logic 86 is applied to acascade of buffer amplifiers in output buffer 84 to help match theoutput impedance of the logic circuitry to the input impedance of themodulation inverter 82. The output of the buffer amplifiers in outputbuffer 84 is applied to the input of the modulation inverter 76.Specifically, the signal TAG OUTPUT is applied to the gate of the drivetransistor associated with modulation inverter 82. Modulation inverter82 then modulates the Q of the tank formed by inductor 78 and capacitor96 to provide amplitude modulation of the carrier signal. In thismanner, the received buffer output is conveyed to reader unit 68 so thatreader 72 can read the identification code. In particular, reader 72processes the signal received at L_tap via inductor 76.

FIG. 12 is a circuit diagram further illustrating reader 72 associatedwith the circuit/reader system 68 of FIG. 10. Reader 72 receives, viaL_tap, a signal containing the carrier signal, e.g., at 125 kHz,modulated by the TAG OUTPUT signal, which may be on the order of 1 kHz,depending on the frequency of clock circuit 88. A low junctioncapacitance signal diode 102 is used to demodulate the signal. A lowpass filter section 98 removes the carrier frequency, and may includeinductor 104, capacitor 106, resistor 108, inductor 110, capacitor 112and resistor 114. An amplifier stage 100 includes an amplifier 116 in anon-inverting configuration, with resistor 118 and feedback resistor 120coupled to the inverting input.

FIG. 13 is a circuit diagram illustrating a thin film transistor-basedinverter circuit 122 that is powered by a partially rectified ac powerwaveform to drive a liquid crystal (LC) display element 124. In theexample of FIG. 13, inverter circuit 122 conforms substantially toinverter circuit 16A of FIGS. 2 and 3. However, the output of inverter16 drives a liquid crystal display element 124. In particular, oneelectrode of liquid crystal display element 124 is coupled to the sourceof load transistor 28 and the drain of drive transistor 30. The otherelectrode of liquid crystal display element 124 is coupled to ground. Asshown in FIG. 13, inverter circuit 16 is powered by partialrectification stage 14, and therefore receives at the common gate/drainconnection of load transistor 28, a partially rectified ac powerwaveform. In order to drive a full LCD, an inverter similar to inverter16 may be provided for each element of the LCD.

FIG. 14 is a circuit diagram illustrating an ac-powered thin filmtransistor-based inverter circuit 126 that drives a light emitting diode(LED) 128. Inverter circuit 16 conforms substantially to invertercircuit 16A of FIGS. 2 and 3, but drives an LED 128. The cathode of LED128 is coupled to the source of load transistor 28 and the drain ofdrive transistor 1308, and the anode of the LED is coupled to ground.

The invention can provide a number of advantages. For example, logiccircuitry powered by a partially rectified ac waveform, and particularlyOTFT-based logic circuitry, may exhibit satisfactory performancerelative to dc-powered thin film transistor circuitry. In the case of aring oscillator, for example, thin film transistor circuitry powered bya partially rectified ac waveform may maintain satisfactory oscillationamplitudes relative to dc-powered thin film transistor circuitry.

As an advantage, the use of a partially rectified ac power waveform todirectly power logic circuitry may eliminate the need for a full waverectifier component or half-wave rectifier component with a filteringcapacitor otherwise required in many applications for delivery of dcpower to the circuitry. Accordingly, by eliminating the need for aconventional rectifier component, the use of partially rectified acpower may reduce the manufacturing time, expense, cost, complexity, andsize of components carrying thin film transistor circuitry.

For circuits, as a particular example, the use of ac-powered thin filmcircuitry may substantially reduce the cost and size of the tag byeliminating much of the components typically associated with an ac-dcrectifier stage, including diode or transistor bridges, and largefiltering capacitors. By reducing the complexity of the rectifier stage,thin film logic circuitry powered by a partially rectified ac waveformcan result in substantial cost and size savings in the design andmanufacture of the circuit.

Thin film transistors useful in forming logic circuitry powered by apartially rectified ac waveform, as described herein, may take a varietyof forms and may be manufactured using various manufacturing processes.For example, the thin film transistors may include organicsemiconducting material, inorganic semiconducting material, or acombination of both. For some applications, organic and inorganicsemiconducting materials can be used to form CMOS thin film transistorcircuitry.

Thin film transistors useful in forming logic circuitry powered by apartially rectified ac waveform as described herein may include, withoutlimitation, thin film transistors manufactured according to thetechniques described in U.S. Pat. Nos. 6,433,359 and 6,616,609;U.S.Patent Publication No. 2003/0207505, published Nov. 6, 2003; U.S. patentapplication Ser. No. 10/012,654, filed Nov. 2, 2001, U.S. patentapplication Ser. Nos. 10/076,003, 10/076,174 and 10/076,005 all filedFeb. 14, 2002, and U.S. patent application Ser. No. 10/094,007, filedMar. 7, 2002, the entire content of each is incorporated herein byreference.

Various modification may be made without departing from the spirit andscope of the invention. For example, although specific examples ofpartial rectification stages have been described, other partialrectification stages may be provided to achieve similar partialrectification results. Moreover, a variety of logic circuitry maybenefit from the use of a partially rectified waveform to power thelogic circuitry. Accordingly, the examples described herein should notbe taken as limiting of the scope of the invention. These and otherembodiments are within the scope of the following claims.

1. A radio frequency identification (RFID) tag comprising: a first andsecond transistors arranged to form a logic gate, a radio frequency (RF)converter that converts RF energy to an alternating current (ac) powerwaveform, a partial rectification stage to produce a partially rectifiedac power waveform from the ac power waveform and directly power thelogic gate with the partially rectified ac power waveform, wherein peaksof half-cycles of the partially rectified ac power waveform havesufficient voltages to power the logic gate, the partial rectificationstage produces an average direct current (dc) voltage that isinsufficient to power the logic gate, and the ac power waveform has aperiod less than a propagation delay of the logic gate.
 2. The circuitof claim 1, wherein the partial rectification stage includes an outputfiltering capacitor.
 3. The circuit of claim 1, wherein the partialrectification stage does not include an output filtering capacitor. 4.The circuit of claim 1, wherein the partial rectification stage includesa half-wave rectifier with insufficient capacitive filtering to producea primarily direct current (dc) power signal as the partially rectifiedac power waveform.
 5. The circuit of claim 1, wherein the partialrectification stage includes a transistor-based rectifier.
 6. Thecircuit of claim 1, wherein the partial rectification stage includes adiode-based rectifier.
 7. The circuit of claim 1, wherein the logic gateincludes one of an inverter, a NOR gate, and a NAND gate.
 8. The circuitof claim 1, wherein the logic gate forms an analog amplifier.
 9. Thecircuit of claim 1, further comprising a display element, wherein thelogic gate is coupled to drive the display element.
 10. The circuit ofclaim 1, wherein the circuit includes a series of inverter stages, theinverter stages being coupled to form at least part of a ringoscillator.
 11. The circuit of claim 1, wherein at least one of thetransistors is an organic thin film transistor.
 12. The circuit of claim1, wherein the semiconductor material of at least one of the transistorsis one of pentacene, zinc oxide, polysilicon or amorphous silicon. 13.The circuit of claim 1, wherein the first transistor is an n-channeltransistor and the second transistor is a p-channel transistor.
 14. Thecircuit of claim 1 wherein at least one of the transistors is aninorganic thin film transistor.
 15. A radio frequency identification(RFID) system comprising: a) the RFID tag of claim 1, and b) an RFIDreader that transmits RF energy to the RFID tag for conversion by saidRF convertor, and reads the information conveyed by said modulator.